1. Field of the Invention
The present invention relates to a display device and a portable terminal. In particular, the invention relates to a portable terminal having a display device in which images are displayed by controlling multiple pixels arranged in matrix. More particularly, the invention relates to a portable terminal having a flat-panel display device in which images are displayed by using multiple thin film transistors provided over an insulating substrate.
2. Description of the Related Art
In recent years, RFID (Radio Frequency IDentification) tags have been researched and developed as a new technology for goods identification and management in the distribution industry as an alternative to conventional barcodes, and also examined as a new personal identification means. Further, it is drawing attentions as a fundamental technology for advancing IT and automation of the infrastructure (cf. Japanese Patent Publication No. Sho62-43238). RFID tags are also called RF chips, RF tags, IC (Integrated Circuit) chips, IC tags, wireless chips, wireless tags, electronic chips, electronic tags, wireless processors, wireless memories and the like.
RFID tags have various advantages in that wireless communication with a reader/writer is enabled by providing an antenna in an IC chip used as the tag, and multiple objects can be concurrently identified unlike a barcode as a typical conventional identification means that requires objects to be directly read out with a scanning barcode reader one by one.
Further, there is an RFID tag that has no internal power source but has an antenna portion for detecting electromagnetic waves transmitted from a reader/writer, based on which direct current (hereinafter referred to as DC) power is generated to operate the RFID tag.
Portable terminals such as a portable phone or a PDA (Personal Digital Assistant) are required to be further reduced in weight and size for improving the convenience. Therefore, each component of the portable terminals is required to be further reduced in volume. For a display device to be an interface portion, a flat panel display is mainly adopted where circuits are configured with multiple thin film transistors (TFTs) provided over an insulating substrate formed of glass, plastic or the like.
Further, in accordance with the improved performance of portable terminals per se, possibility of users carrying the portable terminals has been expanding, and thus a longer continuous operating time is required as compared to the conventional ones.
In order to increase the continuous operating time of portable terminals, each component of the portable terminals is required to be reduced in power consumption, and a battery is required to be increased in capacity. In order to achieve the former requirement for the longer continuous operating time, various measures have already been taken such as lowering the driving voltage or controlling the portable terminals to enter a standby mode often by software control with an aim to reduce power consumption. However, as for the later requirement for the increased capacity of the battery, the volume of the battery is increased if the capacity of the battery is increased; therefore, there arises a trade-off between the increased capacity of the battery and the aforementioned reduction in size and weight.